The present invention is directed generally to logical volume management of data storage resources in a data processing system, and more particularly, to improvements in the dynamic allocation and use of physical data storage devices containing portions of a logical unit of undivided storage.
Commonly assigned U.S. Pat. No. 5,129,088, entitled "Data Processing Method To Create Virtual Disks From Non-Contiguous Groups Of Logically Contiguous Addressable Blocks Of Direct Access Storage Device," and commonly assigned U.S. Pat. No. 5,435,004, entitled "Computerized System And Method For Data Backup," are directed to a system and method of logical volume management in which a plurality of physical partitions or clusters, each representing one or more blocks or sectors of a direct access storage device (DASD), are grouped together and called a physical volume. A plurality of physical volumes are grouped together and referred to as a physical volume group. When a group of related files is to be installed on the system, an aggregate of logically contiguous, undivided storage, known as a logical volume, is created. The logical volume includes a sequence of logical clusters that correspond to one or more of the physical clusters in one or more of the physical volumes of a single physical volume group. The physical clusters and volumes need not be physically contiguous and may even be located on different storage devices. Each logical volume is initially assigned a minimum number of physical clusters as required to store the file group. If additional physical clusters are required to increase the size of the logical volume, they can be added dynamically.
The notion of undivided, logically contiguous storage means that higher-level services (e.g. file systems, data base management systems and other data managers) are presented with a logical view of storage that masks physical device boundaries and provides extended storage attributes for performance and reliability. To the higher level services, it appears as if there is undivided, contiguous physical storage of variable size available. To administer this data storage scheme, the logical volume management system of U.S. Pat. Nos. 5,129,088 and 5,435,044 generates tables of metadata information and stores them on the physical storage devices. The metadata information defines the allocation of physical clusters, physical volumes and physical volume groups to the logical volumes and logical clusters. The metadata information includes information about each participating area of the physical devices. This information is fully replicated and stored on each participating physical device when the system is first initialized and whenever physical clusters are added to or removed from a logical volume.
One of the drawbacks of maintaining metadata information in a fully replicated way on each physical storage device comprising a logical unit of administration is that update performance is compromised because updating the metadata information across all of the participating physical devices consumes processor time. In addition, adverse space occupancy characteristics are experienced because the replicated metadata occupies disk space that could otherwise be used for data. Another drawback of full metadata replication is that the presence of failed or nonoperational devices degrades administrative and data access operations involving only operational devices. When administering a set of physical devices to form logical aggregates of undivided storage, there is the desire to have the data stored in them available to applications and data managers even in the presence of failed or unavailable physical devices. It is desirable to avoid operation in a degraded mode as a result of such non-operational devices. A degraded mode of operation could result if the logical volume management system sensed the presence of a failed or unavailable device during administrative or data access operations and either terminated the operation or proceeded with the operations using excessive error checking.
Accordingly, a need exists for a logical volume management scheme in which the foregoing disadvantages are overcome. What is required is a system and method that reduces the processing time required for administrative operations, increases available storage space, and provides normal administrative and data access operations to all parts of a logical unit of undivided storage that are present in operational devices, regardless of how many parts may be in non-operational devices.